1. Field of the Invention
The present invention relates to a safety device for an electric installation protection apparatus capable of detecting a residual differential current; the safety device is of the type adapted for detecting a break in the neutral without discontinuity of supply and for this it is connected to a phase conductor and to a neutral conductor belonging to an AC distribution network.
The invention is applicable to differential protection apparatus protecting against direct or indirect contacts, such apparatus being adapted to obtain cut off and/or signalling. The invention is preferably applied to networks whose neutral, distributed and separated from the protection conductor, is grounded.
2. Description of the Prior Art
To increase the safety in use of a differential protection apparatus, it is known to associate with such as apparatus a supply device with rectifier circuit having a terminal for connection with the phase conductor, a terminal for connection with the neutral conductor and a terminal connected to ground through a second rectifier circuit; this circuit therefore allows the differential current detector to be supplied with power in the case of a break in the neutral provided there is redundance of the rectifier circuit.
Such a device has a main disadvantages the need to duplicate the rectifier circuit and, for detecting the absence or disappearance of the neutral, requires a specific means such as a special winding on the differential current detection core, or else a resistor disposed in the wire connecting the ground connection to the second rectifier circuit and a voltage/current converter means devoted solely to this detection function, or else a special signalling device.
The aim of the present invention is more especially to overcome such drawbacks by providing a safety device for a differential protection apparatus which allows the differential current detector to be used for detecting in a simple way the absence of a neutral while continuing to supply the rectifier bridge with power without requiring the addition of other detector or rectifier elements.
It also aims at providing positive reliability of operation of the protection device in the case of a fault current and/or break in the neutral.